1. Technical Field
The present disclosure relates to a variable-flow-rate valve mechanism that opens and closes an opening of a gas-flow-rate variable passage for adjusting a flow rate of exhaust gas supplied to a turbine wheel side in a turbocharger such as a vehicular turbocharger, and a turbocharger including the variable-flow-rate valve mechanism.
2. Description of the Related Art
As measures for preventing an excessive rise in a turbocharging pressure by a vehicular turbocharger (hereinafter, simply referred to as a turbocharger), usually, the turbocharger is provided with a bypass passage and a waste gate valve. The bypass passage is formed inside a turbine housing of the vehicular turbocharger, and bypasses a part of exhaust gas from a turbine wheel (a turbine impeller). The waste gate valve is provided at an appropriate position of the turbine housing, and opens and closes an opening of the bypass passage. Here, the bypass passage is one of gas-flow-rate variable passages that adjust a flow rate of the exhaust gas supplied to the turbine wheel side. The waste gate valve is one of variable-flow-rate valve mechanisms that open and close an opening of the gas-flow-rate variable passage.
A general configuration of the waste gate valve will be explained. A support hole is formed by penetrating through an outer wall of the turbine housing. A stem is rotatably supported by the support hole. A base end (one end) of the stem projects outside the turbine housing. In addition, a link member is provided integrally with the base end of the stem. The link member swings around an axial center of the stem in normal and reverse directions by driving actuator.
As shown in FIG. 1, an attachment member 153 is provided integrally with a tip (the other end) of the stem. An attachment hole 155 is formed by penetrating through the attachment member 153. In addition, a valve 157 is provided fitted in the attachment hole 155 of the attachment member 153. The valve 157 is allowed to have backlash to the attachment member 153 (an inclination to a center line C′ of the attachment hole 155 of the attachment member 153 is included). Furthermore, the valve 157 includes: a valve body 161 that can abut against and separate from a valve seat on the opening side of the bypass passage; and a valve shaft 163 provided integrally with a center of the valve body 161, and fitted in the attachment hole 155 of the attachment member 153. Here, backlash of the valve 157 to the attachment member 153 is allowed, and thus followability (adhesion) of the valve 157 (valve body 161) to the valve seat on the opening side of the bypass passage is secured. Furthermore, a clasp 167 for making the valve 157 non-detachable from the attachment member 153 is provided integrally with a tip of the valve shaft 163.
Accordingly, when the turbocharging pressure (a pressure on an exit side of a compressor wheel (a compressor impeller)) reaches a setting pressure during operation of the turbocharger, the link member swings in the normal direction (one direction) by driving the actuator. The stem rotates in the normal direction by the swing of the link member in the normal direction. The valve swings in the normal direction by rotation of the stem in the normal direction, and the valve body 161 separates from the valve seat on the opening side of the bypass passage. As a result, the opening of the bypass passage is opened by a waste gate valve 137, a part of exhaust gas is bypassed from the turbine wheel, and a flow rate of the exhaust gas supplied to the turbine wheel side decreases.
In addition, when the turbocharging pressure becomes less than the setting pressure after the opening of the bypass passage is opened, the link member swings in the reverse direction (the other direction) by driving the actuator. When the stem rotates in the reverse direction by the swing of the link member in the reverse direction, the valve 157 swings in the reverse direction, and the valve body 161 abuts against the valve seat on the opening side of the bypass passage. As a result, the opening of the bypass passage is closed by the waste gate valve 137, and the flow rate of the exhaust gas supplied to the turbine wheel side increases.
Note that Japanese Patent Laid-Open Publication No. 2009-236088 and Japanese Patent Laid-Open Publication No. 2008-101589 show conventional technologies in relation to the present disclosure.